The present invention relates to a reflection sensor used for detecting presence of a detection object. More specifically, the present invention relates to a reflection sensor surface-mounted on a substrate.
As a sensor for detecting presence of a detection object, a contact sensor incorporating a micro-switch and a non-contact sensor such as a photo-interrupter are used conventionally. Generally, the photo-interrupter includes so-called transmission photo-interrupters and reflection photo-interrupters. The transmission photo-interrupter comprises a light emitting element and a light receiving element faced to each other. On the other hand, the reflection photo-interrupter comprises the light emitting element and the light receiving element faced in a same direction.
Recently, demand for the reflection photo-interrupter is greater than for the transmission photo-interrupter. A reason for this is that the reflection photo-interrupter has a construction which allows mounting on a greater variety of locations than does the transmission photo-interrupter.
Now, a conventional reflection sensor (photo-interrupter) will be described with reference to FIG. 9 to FIG. 21. A reflection sensor 1 shown in the figures has a generally rectangular parallelepiped protective package 2 (FIG. 19), in which a light emitting element 31 and a light receiving element 32 are buried (FIGS. 20 and 21).
The protective package 2 includes a first resin body 21 enclosing the light emitting element 31, a second resin body 22 enclosing the light receiving element 32, and a third resin body 25 for holding these two resin bodies 21, 22. As shown in FIG. 19, the first and the second resin bodies 21, 22 have respective upper surfaces exposed to outside, but the other surfaces are covered by the third resin body 25.
The first and the second resin bodies 21, 22 are transparent, allowing light to pass through. The first and the second resin bodies 21, 22 are formed of an epoxy resin for example. On the other hand, the third resin body 25 is non-transparent and therefore does not allow the light to pass through. The third resin body 25 is formed of a black PPS (polyphenylene sulfide) for example.
The epoxy resin has a linear expansion coefficient of 11xcx9c12xc3x9710xe2x88x925/xc2x0 C. for example, whereas the PPS has a linear expansion coefficient of 6xcx9c7xc3x9710xe2x88x925/xc2x0 C. for example. Therefore, when heated, the first and the second resin bodies 21, 22 made of the epoxy resin expand at a greater rate than does the third resin body 25 which is made of the PPS.
As shown in FIG. 20, the light emitting element 31 is electrically bonded to a lead 5a, and electrically connected to another lead 5b via a wire 4a. Likewise, the light receiving element 32 is electrically bonded to a lead 5c, and electrically connected to another lead 5d via a wire 4b. The leads 5axcx9c5d have free end portions soldered to electrode pads P provided on a substrate S respectively. The soldering can be achieved by using a solder re-flow method to be described here below.
First, solder paste H is applied to each of the electrode pads P. Next, the reflection sensor 1 is placed on the substrate S so that the free end portions of the leads 5axcx9c5d are located on the corresponding electrode pads P. The substrate S and the reflection sensor 1 in this state is brought in a heating furnace and heated. The temperature in the heating furnace at this time is not lower than 200xc2x0 C. for example. Thus, the applied solder paste melts thereby wetting the free end portions of the leads 5axcx9c5d and the electrode pads P. Then, the substrate S and the reflection sensor 1 is taken out of the heating furnace and allowed to cool, so that the solder paste sets to fix the reflection sensor 1 onto the substrate S.
The conventional reflection sensor 1 with the above described construction is known to have the following problems.
Specifically, as has been described earlier, the first and the second resin bodies 21, 22 thermally expand at a greater rate than does the third resin body 25. However, the first and the second resin bodies 21, 22 are surrounded by the third resin body 25 except for the respective upper surfaces. Therefore, when the reflection sensor 1 is heated, the first and the second resin bodies 21, 22 expand only in an upward direction as indicated by a dashed line in FIG. 20. When the resin bodies 21, 22 expand only in one direction as in the above, the wire 4a, 4b can be pulled off the lead 5b, 5d respectively.
Further, the conventional reflection sensor 1 has the following problem. Specifically, as has been described earlier, the reflection sensor 1 is heated to the temperature not lower than 200xc2x0 C. in the heating furnace, and then cooled. During the cooling, the molten solder paste H becomes solid at a temperature of about 180xc2x0 C. for example, fixing the leads 5axcx9c5d onto the electrically conductive pads P. However, at this particular point (at the temperature of 180xc2x0 C.), the protective package 2 (especially the first and the second resin bodies 21, 22) is still in a thermally expanded state in a course of thermal shrinkage with ongoing decrease in temperature.
If the protective package shrinks while the leads 5axcx9c5d have been fixed onto the conductive pads P, a force to pull the leads 5axcx9c5d off the protective package 2 is exerted. This generate excessive stress on the wires 4a, 4b, and can pull the wires 4a, 4b off the leads 5axcx9c5d. 
It is therefore an object of the present invention to provide a reflection sensor capable of solving the above described problem.
A reflection sensor provided by a first aspect of the present invention comprises:
a light emitting element;
a light receiving element cooperative with the light emitting element;
a first resin body enclosing the light emitting element and including a first surface and a second surface away from the first surface;
a second resin body enclosing the light receiving element and including a third surface and a fourth surface away from the third surface;
a third resin body holding the first and the second resin bodies;
a first pair of leads electrically connected to the light emitting element;
a second pair of leads electrically connected to the light receiving element;
wherein the first surface and the second surface of the first resin body and the third surface and the fourth surface of the second resin body are respectively exposed to outside.
According to the arrangement as described above, each of the first resin body and the second resin body can thermally expand uniformly in upward and downward directions. Therefore, it becomes possible to effectively prevent unwanted stress from developing within the first resin body and the second resin body.
According to a preferred embodiment of the present invention, the first and the second resin bodies are transparent whereas the third resin body is non-transparent. Here, the term xe2x80x9ctransparentxe2x80x9d is used for a case in which the resin body allows a predetermined light to pass through. Therefore, if a resin body which looks black to human eyes allows an infrared ray for example, the resin body is described as xe2x80x9ctransparentxe2x80x9d to the infrared ray.
According to the above preferred embodiment, the first and the second resin bodies have a thermal expansion coefficient larger than that of the third resin body.
Preferably, the first and the second resin bodies are formed of an epoxy resin whereas the third resin body is formed of a heat resistant resin.
Preferably, the second surface of the first resin body provides a bottom surface of the first resin body whereas the fourth surface of the second resin body provides a bottom surface of the second resin body.
Preferably, the bottom surface of the first resin body and the bottom surface of the second resin body are covered only partially by the third resin body.
The leads of the first pair and the second pair have respective free end portions flush with the bottom surface of the second resin body. According to the arrangement as above, the reflection sensor can be easily fixed on a substrate by means of a solder re-flow method for example.
A reflection sensor provided by a second aspect of the present invention comprises:
a light emitting element;
a light receiving element cooperative with the light emitting element;
a first resin body enclosing the light emitting element and including an upper surface and a bottom surface away from the upper surface;
a second resin body enclosing the light receiving element and including an upper surface and a bottom surface away from the upper surface;
a third resin body holding the first and the second resin bodies;
a first pair of leads electrically connected to the light emitting element;
a second pair of leads electrically connected to the light receiving element;
wherein the leads of the first pair and the second pair are respectively provided with engaging means for engagement with the third resin body whereby preventing the leads from displacement with respect to the third resin body.
According to the arrangement as the above, even if the leads of the first pair and the second pair come under an unwanted tension, the leads are not displaced with respect to the third resin body.
According to a preferred embodiment of the present invention, the leads of the first pair are formed with projecting portions extending from the first resin body into the third resin body. Further, the leads of the second pair are formed with projecting portions extending from the second resin body into the third resin body into the third resin body.
According to another embodiment of the present invention, the leads of the first pair and the second pair are respectively formed with projecting portions at locations where the leads cross the third resin body.
According to still another embodiment of the present invention, the leads of the first pair and the second pair are respectively formed with cutouts at locations where the leads cross the third resin body.
According to still another embodiment of the present invention, the leads of the first pair and the second pair are respectively formed with bent portions at locations where the leads cross the third resin body.
According to still another embodiment of the present invention, the upper surface and the bottom surface of the first resin body, and the upper surface and the bottom surface of the second resin body are exposed outside.